Djokovic, who had already voiced his opposition to the blue clay, was left fuming over the condition of center court, which he said was completely different to the practice courts he trained on before the event.

"To me that's not tennis. Either I come out with football shoes or I invite Chuck Norris to advise me how to play on this court," said Djokovic, who like Rafael Nadal has been critical of the new-look surface. "Center court is impossible to move on. I hit five balls throughout the whole match. With everything else, I was just trying to keep the ball in the court."

The ATP reiterated that the new surface is in a test period this year, and that a decision on whether to use it again will be made after this event.

The defending champion was cruising until the second set when his 137th-ranked Spanish opponent broke for 2-1. Djokovic then made four straight unforced errors in his next service game -- including two double faults -- to go down 4-1.

Djokovic complained about the surface throughout, but managed to get his emotions in check and his game together to take a decisive 4-2 lead in the third set before sealing his 25th match win of the season.

"When you slide on the red clay you have a feeling you can stop and recover from that step. But here, whatever you do ... you are always slipping," said Djokovic, who hit 20 winners to 24 unforced errors. "Not a single player -- not woman, not man -- I didn't hear anyone say 'I like blue clay.' "

Azarenka has already won four titles this year, including the Australian Open, but showed less convincing form on the blue surface.

"I felt like a lost a little bit of my concentration," Azaranka said. "I didn't adjust well to some of the obstacles that happened but I'm glad that I could turn it around pretty quickly and finish the match in my favor."

The Belarusian took the opening set without too many worries before stumbling toward the end of the second set as she double-faulted to be broken for Hlavackova to tie it up 5-5.

Azarenka saved set point with a forehand smash and took it to the tiebreaker, where she took a 5-1 lead before clinching it when Hlavackova -- who had needed treatment on her left thigh late in the second set -- hit long.

"Sometimes you have these roller coasters and she is one those players that doesn't allow you a rhythm," Azarenka said, who is playing her second clay court event this season after losing to Sharapova in the Stuttgart final. "I'm glad I could stay in control and finish the match. There is more room to improve."

Sharapova was more convincing in her second-round match, as Zakopalova's erratic serve opened her up to Sharapova's solid ground strokes. Sharapova earned the first of five breaks in the opening game and was in command after another break gave her a 4-1 lead.

Zakopalova came forward to break back in the next game but could get no closer as the pair held serve before Sharapova clinched the set with one of four aces.

Zakopalova was overpowered again on her opening serve but saved a match point and broke back to get to 5-3 before her seventh double-fault clinched it for Sharapova.